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About this book

This book comprises the proceedings of the conference “Future Production of Hybrid Structures 2020”, which took place in Wolfsburg.

The conference focused on hybrid lightweight design, which is characterized by the combination of different materials with the aim of improving properties and reducing weight. In particular, production technologies for hybrid lightweight design were discussed, new evaluation methods for the ecological assessment of hybrid components were presented and future-oriented approaches motivated by nature for the development of components, assemblies and systems were introduced.

Lightweight design is a key technology for the development of sustainable and resource-efficient mobility concepts. Vehicle manufacturers operate in an area of conflict between customer requirements, competition and legislation. Material hybrid structures, which combine the advantages of different materials, have a high potential for reducing weight, while simultaneously expanding component functionality. The future, efficient use of function-integrated hybrid structures in vehicle design requires innovations and constant developments in vehicle and production technology. There is a great demand, especially with regard to new methods and technologies, for "affordable" lightweight construction in large-scale production, taking into account the increasing requirements with regard to variant diversity, safety and quality.

Table of Contents

Frontmatter

Innovative and Smart Production

Frontmatter

Life Cycle Assessment of Thermoplastic Hybrid Structures with Hollow Profiles

The combination of innovative materials, process chins and intelligent material-adapted design concepts enables an efficient part production for future mobility applications. Hybrid structures made of thermoplastic pre-impregnated composite (TPC) sheets and injection moulding bulk material have already crossed the threshold to series production. Thanks to a newly developed production technology, hollow profiles with continuous fibres can now also be integrated into thermoplastic composite hybrid structures in the sense of a modular design system. However, the resource consumption of such hybrid structures has not yet been investigated.This contribution describes the set-up and life cycle analysis (LCA) of a highly automated manufacturing process for the production of complex crash-loaded vehicle structures in thermoplastic composite design. The concept bases on the production of a hollow profile made of hybrid yarn, which is subsequently overmoulded and combined with a TPC sheet in an injection moulding process. For the hollow profile manufacturing, a novel automated preforming technology is used. The textile preform is then consolidated in a variothermal consolidation station, consisting of a temperature control system and an additively manufactured consolidation tool. For the subsequent overmoulding of the hollow profile, methods for stabilising the hollow profile were studied and implemented in an injection moulding complex. A plasma system for activating the surface of the hollow profile was used to create a permanent joint between the hollow profile and TPC sheet. At the example of a backrest with an integrated seat belt, the technology and its potential application in crash-relevant structures was proven.In addition to the process set-up, manufacturing studies were carried out with the aim of evaluating the ecological potential of the process chain. For this purpose, a cradle-to-gate approach was chosen, in which the process-related energy consumption as well as the material consumption were measured and used for LCA. Thus, the most relevant process steps can be identified and possibilities for increasing efficiency can be derived.

Alexander Liebsch, Michael Müller-Pabel, Robert Kupfer, Maik Gude

Interdisciplinary Research for the Development and Realization of a Structural Component in Multi-Material Design Suitable for Mass Scale Production

Lightweight design offers a reduction of local emissions and increase the range and handling dynamic of automobiles while driving. With a 40% share of the total vehicle mass, the body-in-white, consisting of high-strength steel materials, is a significant lever for weight reduction, but it is reaching its limits as the sheet thickness is further reduced, especially in crash-relevant structures such as A- or B-pillars, bumper cross beams e.g. (Friedrich in Leichtbau in der Fahrzeugtechnik, Springer, ATZ/MTZ-Fachbuch. Wiesbaden, 2017; Liu et al. in Int. J. Adv. Manuf. Technol. 69:211–223, 2013). An alternative approach are hybrid structures made of a combination of fibre-reinforced plastics (FRP) and metal sheets. The standard metal components can be improved by the targeted use of FRP in many ways. It enables a production of completely new components with increased performance and higher level on functional integration. This paper describes the transition of a lower A-pillar of a high-volume segment vehicle by showing the changeover from the monolithic steel design to the hybrid plastic-metal design. Therefore, the conceptual design of the component and its production are explained.

Benjamin Bader, Werner Berlin, Michael Demes

Net Shape Stacking and Consolidation of Thermoplastic Composite Tapes

Thermoplastic composite tapes are produced with a specific width, e.g. 300 or 600 mm. A common production method is first to slice the tape rolls into narrow tapes bands with a width of e.g. 50 mm. These narrow tapes are used for stacking operations. Upon using such a technology, it is necessary to combine several narrow tapes to end up with a single layer. The outer edges of the tape stack normally extrude beyond of the area needed for the part, meaning, a cutting operation is necessary, either right after the stacking or after the consolidation. A beneficial alternative approach starts with large cutouts from the rolls, which are obtained by efficient stamping. These cutouts cover as much area as possible in one piece. The idea is to use the full tape width, if possible. The cutouts are stored in automatized magazines and become stacked efficiently employing a pick-&-place approach. The use of image processing enables precise adjustment of the gaps and overlaps.This net-shape stacking technology leads to stacks that consist of a minimum number of tape cutouts. Even different types of tapes can be combined. The net-shape stacking is followed by an also net-shape consolidation in a heating-&-cooling unit. Both, the stacking unit as well as the consolidation unit are capable producing stacks and blanks within a typical injection moulding cycle time of one minute. The consolidated blanks fulfil the requirement of a best fit outer contour, which can be draped into the desired shape of the final part. Furthermore, the tailored composite blanks may expose the distinct variations in thickness and fibre orientation, which is optimized for the final part’s specific loading conditions.

Paul Zwicklhuber, Norbert Müller

Thermoset Technologies for Cost Efficient Production of Lightweight Composites

The automotive industry is evolving rapidly with increasingly rigorous emission targets and leaps toward electrification and autonomous driving. These forces continue to trigger lightweight solutions, advancing the adoption of novel composite materials for diverse applications. Composite materials have been used for body parts in sports and luxury vehicles for a long time, enabling design freedom, astonishing aesthetics and leading-edge driving performance. This extended abstract discusses state of the art composite manufacturing processes enabling cost-efficient high-quality parts production.

Lars Moser, Sigrid Heide, Ian Swentek, Uwe Schmidt, Manuel Seiz

Factories of the Future

Frontmatter

Contribution to Digital Linked Development, Manufacturing and Quality Assurance Processes for Metal-Composite Lightweight Structures

More and more effort in development processes is required to meet the constantly increasing demands on technical components. Especially in hybrid structures, the high number of degrees of freedom in development due to the different material properties and interactions between them leads to complex and multi-disciplinary processes. Digitalisation is one option to meet the increasing demands for shorter development times and more efficient products. In addition, hybrid structures require a generally applicable procedure and guidelines for the design and preliminary dimensioning to support the engineering. A novel approach is presented to digitally link the development steps to create an interactive development process and a structure for a holistic data analysis. This is exemplary shown for an open, ribbed profile made of hybrid metal-composites in a module-based scheme. For a pre-dimensioning solution of the cross-section profile, analytical models, linked to adaptable numerical models, have been build up and transferred in the process model. Moreover, experimental validation concepts for the bending properties of a car body component is presented.

Daniel R. Haider, Fabian Folprecht, Johannes Gerritzen, Michael Krahl, Sebastian Spitzer, Andreas Hornig, Albert Langkamp, Maik Gude

Thinking Innovation Ahead – Joint Semantic Modelling for Integrated Product and Production at the Research Campus Arena2036

The goal of the Research Campus ARENA2036 is, based on excellent, interdisciplinary basic and applied research, to produce potentially disruptive and leap-frog innovations, to transfer them to industry, and thus to contribute to the active shaping of work, mobility, production of the future, and digitization. The seamless transfer of research results into industrial application is intended to increase the competitiveness of the business location Baden-Württemberg and to enable the creation of novel business models – especially for SMEs. An essential component here is the interdisciplinary and trans-institutional approach of various fields of science and application, which is reflected in the close cooperation of all actors under the umbrella of ARENA2036. Based on this basic idea, current research work is carried out in the field of data interoperability in the domains of product development, and production system design. The goal is to achieve a significant overall reduction of product development and market introduction times. This topic is particularly significant due to the currently ongoing transformation processes in the automotive industry, which question the prevailing product and production patterns and require an increasing flexibility of manufacturing processes. New product and production technologies have to be incorporated into serial production at ever shorter intervals, which poses great challenges for both product design and corresponding production systems.This paper conceptually approaches the basic ideas in innovation design incorporated at the Research Campus ARENA2036 as a research platform that allows for joint research in a precompetitive environment thus enabling all partners to think innovation ahead. One example for this, is the holistic semantic modelling of integrated product and production development in the research projects Fluid Production and Digital Fingerprint. Both projects conceive an approach to production that emphasizes the need for constant flexibility qua anthropocentric reconfigurability.

Clemens Ackermann, Manuel Fechter, Peter Froeschle

Integrated Factory Modelling – Enabling Dynamic Changes for the Factory of the Future at the Example of E.GO Mobile AG

Fast-moving changes in products, materials and process technologies require factory planning processes and procedures to be flexible and dynamic. Today, most factory planning projects are missing their budget (72%) and time targets (60%). To reduce these deviations, digitalization is key to success, but in current approaches, coordination between different planning disciplines is missing as well as different technology maturity levels prohibit automated interfaces. The Integrated Factory Modelling (IFM2) is an interdisciplinary planning approach for Green- and Brownfield factories coordinating all planning disciplines from infrastructure to process planning across the factory lifecycle. Therefore, the Integrated Factory Model (IFM) as a single dataset is established for all planning participants, accessible everywhere and on every device. Collaboration is enhanced by the working mode with an agile factory scrum process. Based on the IFM user-specific smart expert tools have been developed supporting planners and managers.As a result, planning processes could be improved significantly, reducing costs by 20–30%, saving one-year planning time for a Greenfield and reduce planning failures significantly. IFM was initially applied and introduced to the e.GO Mobile AG, which is used as an example showing real-life use cases, challenges as well as next development steps.

Peter Burggräf, Matthias Dannapfel, Sebastian Patrick Vierschilling

Life-Cycle Engineering

Frontmatter

Methodology for Assessing the Environmental Impact of Emerging Materials

In order to reduce environmental impacts of product systems through material research and development, to identify mitigation potential, and to avoid problem shifting, information about the environmental impact of emerging materials is needed at an early stage. This information can support decisions on material selection as well as manufacturing process optimization. The goal is to reduce the impact of an emerging material so that it is lower than the impact of an established material. We propose a methodology to address this need. It consists of four steps: 1) reference LCA, 2) forecast LCA of emerging material, 3) scaling and 4) comparison. We apply the methodology to automotive seat cover materials such as bovine leather, faux leather and a fictitious flax-based material, where the production of the latter shares some production steps with leather. The results indicate how much environmental space the to-be-developed manufacturing process of the fictitious material can take up before it surpasses that of leather and faux leather. This way, the methodology can support the material research and development process in identifying and creating alternative materials with a lower environmental impact.

Malte Schäfer, Martina Gottschling, Felipe Cerdas, Christoph Herrmann

Systematic Design of Body Concepts Regarding Mini-Mal Environmental Impacts in an Early Concept Phase

For internal combustion engine vehicles, the use stage dominates the life cycle emissions. In comparison, the life cycle emissions of battery electric vehicles highly depend on the electricity mix. With consideration of an European electricity mix the life cycle emissions split approximately equally between the production and use stage. Approximately 46% of these emissions is caused by the battery production. But the absolute and relative share of emissions from the vehicle production increase as well. Thus both stages have to be considered for the environmental assessment of body parts. Therefore the environmental impact of different material concepts as well as production and joining technologies are in focus of the development. A decision regarding environmentally optimized body concepts has to be made in the concept phase. A first approach provides mass indices from Ashby 1999. So, concepts made out of different materials can be developed in a given design space. These concepts are evaluated using a simplified life cycle assessment, which considers different body designs, mobility concepts and markets (electricity mixes). It can be shown that there is a large variance of greenhouse gas emissions for a given lightweight design potential. Hence, an optimization procedure to find concepts with the lowest environmental impacts is needed. In this paper a first approach for an optimization procedure concerning ecological aspects of body parts is described and demonstrated with an example application.

Lars Reimer, Pavan Krishna Jois, Hartmut Henkelmann, Jens Meschke, Thomas Vietor, Christoph Herrmann

Processing Capabilities for Thermoplastic Composites – Minimum Material Consumption and Recyclability

An important measure for improved lightweight performance is utilisation of materials only to the extent, as it is necessary for the application. To achieve a minimum part weight in high volume lightweight applications, it is necessary to combine thermoplastic composite sheet materials exposing different thicknesses. Then, a minimum material consumption is gained. Such composite components have the capabilities of being fully recyclable. Used parts as well as scrap and cut-off that arises during production can be recycled and used for injection moulding of ribs and other geometry, even to become part of the same composite component later on. However, there are considerable challenges in the processing since different composite sheets need to be processed simultaneously. A processing unit was designed, build and tested that is capable to process thermoplastic composite sheets with three different thicknesses. The resultant part, a structural automotive door component, exposes areas were the composite sheet thickness is 0.6 mm, 1.0 mm, and 2.5 mm, respectively. Besides of the injection moulding, the processing requires two different kind of infrared ovens with a specialized software for the control of the heating and three articulated robots for the automated handling operations of the composite blanks.

Norbert Müller, Philipp Seinsche

Generative Manufacturing

Frontmatter

Evaluation of Technologies for the Fabrication of Continuous Fiber Reinforced Thermoplastic Parts by Fused Layer Modeling

In this research technologies for the production of continuous fiber-reinforced thermoplastics using additive manufacturing are investigated and evaluated. The focus is on the “Fused Layer Modeling” (FLM) process, which is based on an additive, thermoplastic extrusion process. The possibility of combining the plastic filament with continuous fibers allows a specific fiber reinforcement to be introduced into the part to increase the mechanical properties. First, an overview of the technologies for processing continuous fibers is presented. These strategies differ in the design of the machine (hardware) and the possibilities for the constructive insertion of the continuous fibers in slicing (software). The differences of the technologies are the processing method of the fiber as well as the fiber roving used in the extrusion process. The maximal fiber volume content and the interlaminar fiber-matrix adhesion are investigated in various commercial technologies by means of tensile and bending tests. In conclusion, the different technologies are evaluated with regarding the maximal fiber volume content and quality of interlaminar fiber-matrix adhesion.

Daniel Pezold, T. Rosnitschek, A. Kleuderlein, F. Döpper, B. Alber-Laukant

Design of Additively Manufactured Heat-Generating Structures

Multi-material additive manufacturing provides new design freedom for integration of functions and opens new possibilities in innovative product design due to local material variations. In particular, material extrusion (MEX) allows for combination of different industrial-grade thermoplastic materials to enhance the functionality of a product by integration of functions. Thus, for instance, electrically conductive structures or heat-generating surfaces can be incorporated in a part by using conductive polymers filled by carbon black (CB), carbon nanotubes (CNT) or copper nanowires (CNW).The resultant properties of additively manufactured parts are mainly influenced by the choice of process parameters. In addition to mechanical properties (e.g. stiffness and strength), electrical properties are also like resistivity and volumetric power density influenced. In order to design heat-generating structures in a targeted manner, the dependencies between process parameters and electrical performance must be determined. Thus, in this article the dependencies between the process parameters extrusion temperature, raster angle orientation and extrusion speed are investigated experimentally. In order to adjust the resistivity of an additively manufactured part and surface temperature by resistive heating, these dependencies are transferred into mathematical descriptions. The setup of design of experiment is based on model selection for analytical description of material-specific characterization.In order to demonstrate the potential of additively manufactured heating structures by material extrusion a garnish mold with incorporated heating panels is built as multi-material design. Finally, the heating of the prototypical panel is analyzed by thermographic analyses. Thus, the approach for achieving certain surface temperatures by varying process parameters and part geometry based on the mathematical description is validated.

Karl Hilbig, Hagen Watschke, Thomas Vietor

Process Simulation for Screw Extrusion Additive Manufacturing of Plastic Parts

Additive manufacturing of plastic parts is a widely spread production method for prototyping. In the recent past, additionally series applications evolved from different sectors of industry. Especially plasticizing processes are characterised by high printing speed and a broad range of materials which can be provided both as filament and granulate. The latter offers the advantage of lower material costs compared to filaments but requires a screw extruder to plasticise and homogenise the plastic melt prior to its deposition through a nozzle. Screw extruders have a wide processing range and therefore are capable of producing a huge variety of printing bead shapes. This shape is directly affected by several extrusion settings and has a great impact on manufacturing time as well as mechanical properties and surface quality of fabricated parts. It would take great effort to determine the influence of process parameters like temperatures and velocities in experimental trials.In this contribution a process simulation is presented which predicts the bead shape for screw extrusion additive manufacturing. A computation of material flow is performed including nozzle outlet and bead shaping in the gap between nozzle and printing platform. The free surface of the plastic melt is tracked using a volume of fluid method. Numerical investigations follow the concept of Design of Experiments in order to identify significant relationships between extrusion settings and bead shape. By this means, processing windows can be estimated virtually and conclusions can be drawn regarding slicing parameters and manufacturing time.

Johannes Albers, Ulf Hillemann, Andreas Retzlaff, André Hürkamp, Klaus Dröder

Bio-based Innovations

Frontmatter

Biomimetic Soft Robotic Peristaltic Pumping System for Coolant Liquid Transport

In nature and technology, liquids are transported and distributed in a directed manner via pumping systems. Technical pumps often show signs of wear due to abrasion on moving parts, erosion and liquid contamination, which can lead to damage and unwanted noise. Innovative pump systems for electro mobility applications should have particularly low noise emission. In the course of evolution, various solutions have emerged in nature and can serve as a source of inspiration for the development of biomimetic pumping systems. In the last decade, the development of various biomimetic peristaltic systems highlight this pronounced biomimetic potential. These systems are based on principles behind bowel and esophageal peristalsis and incorporated within soft robots and medical devices. The main goal of this study was the biomimetic implementation of peristalsis into a flexible, silent, robust, energy efficient, space-saving and low cost technical application for the usage in combustion engines, electric engines and cooling systems. The biomimetic pump of the present study is based on the esophageal peristalsis and enables an easy, quiet and safe transport of a variety of Newtonian and non-Newtonian fluids with variable viscosities. The characterization of individual actuators as well as the entire peristaltic pump system in terms of closing rate and volume flow proved the influence of the actuator frequency and different peristaltic actuation patterns on the generated flow rate. The results show that the biomimetic flexible and elastic self-priming peristaltic pump based on silicone achieves sufficient flow rates of more than 250 l/h and thus offers an excellent alternative to conventional technical pumps in the field of electro mobility.

Falk J. Tauber, Tom Masselter, Thomas Speck

Biomimetic Suction Cups for Energy-Efficient Industrial Applications

Suctions cups are widely used in industrial applications for handling various goods. In the animal kingdom, a multitude of analogous structures has evolved, e.g. in octopuses and leeches, which allow the respective organisms to securely attach and detach from various substrates. To date, the biological suction cups outperform their technical counterparts in terms of versatility, as they allow attachment also on challenging (e.g. porous, wet and fouled) surfaces.

Harald Kuolt, Tim Kampowski, Simon Poppinga, Thomas Speck, Ralf Tautenhahn, Atena Moosavi, Jürgen Weber, Felix Gabriel, Erika Pierri, Klaus Dröder

Bio-Sourced Artificial Leather for Interior Automotive Applications

Flexible interior artificial leather is today produced on the basis of soft PVC and PUR and to a small extent of polyolefins, whereby the polyurethanes are primarily suitable for high-quality materials.PU-based coating systems have several advantages: The mechanical properties of the coating can be adjusted in a wide range and they are thermally stable. Furthermore, they are considered as a substitute for PVC because they are free from plasticizers.Fraunhofer WKI has developed a series of bio-sourced polyurethane leathers with a bio-sourced proportion of >85 wt.-%. The polymer matrix consists of sugar and vegetable oil derivatives and it is waterborne. The polymer material is UV-curable, providing an improved mechanical performance for the leather as well as an excellent chemical resistance. The elongation at break could be up to 175%, while the bio-source artificial leather is resistant to water and common household chemicals, such as red wine, 48% alcohol, mustard and water. For applications where there is no requirement for highly flexible materials e.g. dashboard lamination or gear stick, we also developed a finish that is resistant to sunscreen. Furthermore, a flexible head rest was designed by memory-wood foam. The final properties of the wood foam are accomplished by a combination of wood and a bio-soured latex to reach a pliable head rest. After the construction of head rest, the material was covered with the bio-sourced polyurethane leather smoothing the surface of the memory-wood foam.

Stefan Friebel, Steffen Sydow

Functional Structures

Frontmatter

Continuous Profile Production with Hybrid Materials by Pultrusion

An important factor for the success of electromobility is lightweight design – the lower the mass of a vehicle, the less energy is required for acceleration and movement, and the smaller, lighter and cheaper battery and drive technology can be designed. In close cooperation with partners from science and industry, the Fraunhofer Institute for Machine Tools and Forming Technology (IWU) develops solutions suitable for series production for a sustainable German automotive industry. Lightweight design in economical hybrid design is the focus of numerous development projects. In the research project “Hybrid Pultrusion”, the research partners Fraunhofer IWU and the Leibniz-Institut für Polymerforschung Dresden e. V. (IPF) develop new methods for the reliable and reproducible production of hybrid components made of metal and fiber-reinforced plastics (FRP) by using the pultrusion process. A central focus in this project is the bonding mechanism between metal and FRP at the molecular level and the transfer of these phenomena to the pultrusion process.

Marcus Knobloch, David Löpitz, David Wagner, Welf-Guntram Drossel

Comparison of the Mechanical Properties of Adhesively Bonded and Mechanically Interlocked Steel/Fibre-Reinforced Thermoplastic Hybrids Produced Using One-Step Forming Process

The continuous increase in the weight of newly registered vehicles is in conflict with the targeted reduction in greenhouse gases emission and fuel consumption imposed by several environmental regulations. To meet these stringent environmental regulations, the fabrication of hybrid structural parts is a particularly suitable alternative for mass-produced vehicles. Through the combination of fibre-reinforced thermoplastics (FRTP’s) and steels, an optimum of component costs and weight savings can potentially be achieved. However, the production of hybrid components traditionally involves additional manufacturing steps and a subsequent joining processes. In order to increase the efficiency of the hybrid production process, both materials can be formed and joined together in one forming step. In this paper, two different approaches to join FRTP and steel sheet in a single forming step are compared in respect of their mechanical strength. For this, structured steel sheets designed to obtain mechanical interlocking and an adhesive film are used. Furthermore, process parameters such as forming force, blank holder force and tool temperature are varied during the manufacturing process to determine their influence on the mechanical performance.

David Trudel-Boucher, Philipp Kabala, Jan Beuscher, Michel Champagne, Klaus Dröder

Thin Film Sensor Systems for Use in Smart Production

For further success of the fourth industrial revolution, it is necessary to acquire detailed process data parallel to data processing. For measuring exact data of the production system, the sensor systems has to be integrated in the decisive area of the production process. This leads to an increasing demand for sensor systems that can directly be applied on tool or component surfaces, which are in high loaded contact with the workpiece or counterpart. For this reason, Fraunhofer IST develops thin film sensor systems by physical vapor deposition (PVD), plasma enhanced chemical vapor deposition (PECVD) and structuring technologies with high hardness, high wear resistance, low friction coefficient and a high load capacity that are very small and only few μm thick. These multisensory thin-film-systems can record force, temperature and their distributions directly in a production system or a tool surfaces with spatial resolution, so that both inline condition monitoring and predictive maintenance are possible. For such a multisensory thin film system the thermoresistive and piezoresistive properties of metal or hard coatings and diamond-like carbon layers (DLC) are used and has to be well adapted and arranged e.g. by structuring processes. Different thin film sensor types, their manufacturing as well as examples for application and the sensor performance in industrial production processes will be introduced. A thin film sensor on a tool segment for injection molding of natural fibre reinforced polymers will be shown. This thin film sensor system with high wear resistance allows measuring the temperature distribution on the mold surface and the monitoring of the melt front movement. A further interesting example are smart washers for static and dynamic control of the true clamping force of screw connections. Prospectively, these various thin film sensor systems could be a capable contribution to establish an intelligent, digitalized and smart production.

A. Schott, S. Biehl, G. Bräuer, C. Herrmann

Radomes – Process Influences on the Integration of Radar Sensors

Intensive research is currently being focused on autonomous driving. Nowadays, comprehensive assistance systems already support the driver and ensure increased safety in road traffic. Core of these systems are well developed sensors that detect the surrounding area and thus ensure the safety of all road users. An important technology in this context is the radar sensor. When integrating it into the vehicle the performance of this sensor is highly dependent on its environment. In this regard the design of the cover of the radar sensor a so-called radome plays an important role. Radomes are supposed to ensure the reliability of the radar sensor by their protective function under consideration of the vehicle design. However, the material of radomes influences the high frequency electromagnetic waves.Therefore, a functional design of radomes requires fundamental knowledge of the interaction of materials and radar waves and thus of the influence of the manufacturing process, the process parameters and the part design. In this paper the structural and process-related influences of injection moulding on damping behaviour of engineering plastics are investigated. A strong relation between thickness and signal damping is observed. Furthermore, a relation between the thermodynamic process parameters of the injection moulding process and the damping behaviour is demonstrated.

Teresa Bonfig, Joachim Sterz, Jan P. Beuscher, Klaus Dröder

Reports from the Research Clusters

Frontmatter

Fiber Orientation Evaluation of Intrinsically Manufactured Metal-CFRP Hybrid Structures by Data Fusion of Pulsed Phase Thermography and Laser Light Section

The intrinsic production of metal-CFRP (carbon fiber-reinforced polymers) hybrid structures allows a load-path-optimal design of connecting components. However, the intrinsic production of complex hybrid 3D parts is prone to defects such as delaminations or fiber misalignments. Fiber misalignments of the woven fabric especially occur in the region of the metal insert. Pulsed phase thermography (PPT) is widely used for non-destructive testing of fiber-reinforced polymers, especially for delaminations. Laser light section (LLS) is suitable for generating a 3D cloud of points (CoP) of the component to be measured. The usage of two laser light section sensors allows in-line measurements of complex 3D geometries by preventing shades. An in-line quality assurance of the finished hybrid component is performed by data fusion of LLS and PPT. The resulting 3D thermographic data can be used to locate and quantify defects. In this contribution, a method for detecting individual fiber bundles in woven fabrics and quantifying the 3D fiber alignment based on the fused LLS and PPT data is presented. This could allow for the simultaneous detection of delaminations and fiber misalignments using the same measurement technology.

Lucas Bretz, Adrian Gärtner, Benjamin Häfner, Gisela Lanza

Combined External and Internal Hydroforming Process for Aluminium Load Introduction Elements in Intrinsic Hybrid CFRP Contour Joints

This paper presents the intrinsic processing technology of a hybrid carbon fibre reinforced thermoplastic/aluminium hollow structure with the focus on a novel two-step hydroforming process of the aluminium load introduction element. An overview in the design of the hydroforming tooling with a combined external and internal pressure application is given. Concepts for sealing the multi-part forming tool for a pressure up to 350 MPa were investigated and validated. Using structurally relevant combinations of meso structures and macro contours, numerical sensitivity analyses were used to determine the relationships between geometric parameters of the shape elements, the material and the process parameters. The most important influences on the hydroforming operation and the geometric limits that can be achieved are presented.

Raik Grützner, Veit Würfel, Roland Müller, Maik Gude

Mesoscale Surface Structures in CFRP-Metal-Hybrid Joints – Aspects of Design and Manufacturing

In light weight construction, the concept of multi-material design allows to benefit from the advantageous properties of different materials. Thereby the joining technique for dissimilar materials must always be taken into account. The joining of carbon fibre reinforced polymers and metals is an example where innovative approaches complement or replace the usual joining technology. A special approach is a metal insert overmoulded with a multifunctional polymer, whereby the surface structures improve the intrinsic properties of the compound. These inserts are produced in an injection moulding process.In this contribution, the forced demouldability of undercuts from mesoscale surface structures is investigated for reinforced and non-reinforced Polyphthalamid (PPA). Simulations predict very high deformations rates for the forced demoulding of the undercuts. In experimental tests, the demouldability of four parts with different angles of inclination (0°, 15°, 30° and 45°) and pins with height of 0.5 mm, 1 mm and 2 mm are examined. Thereby the influence of injection moulding parameters such as melt and mould temperatures is studied by a full factorial Design of Experiments (DoE) analysis. The results show that even undercuts from a 45° inclination angle can be demoulded under certain conditions. The statically evaluation points out that the material reinforcement as well as mould and polymer temperature are the main factors for demouldablitiy of pin undercuts. Finally, an overview of the demoulability of pins is given as a function of the material, pin heights and part inclination angle.

Fabian Günther, Markus Stommel

Nondestructive and Destructive Testing on Intrinsic Metal-CFRP Hybrids

Motivated by legislative and environmental restrictions, cost efficient lightweight design for automotive applications is becoming more and more important. While designing the automotive body completely out of CFRP is too expensive for series production, multi-material hybrid structures represent a good compromise between cost and weight reduction.The presented approach is a CFRP specimen containing an intrinsic aluminium inlay that is overmoulded with a thermoplastic polymer reducing the stiffness difference between the used different materials.Defects like delamination and fibre cracking often are not clearly visible, but have a significant influence on the mechanical properties of fibre-reinforced composites in general and more particularly of such an intrinsic hybrid as presented in this paper. In order to identify and evaluate these defects nondestructive testing can be a powerful tool. Furthermore, a combination of nondestructive and destructive testing methods can be used to develop a better understanding of the damage mechanisms of such a hybrid specimen under various environmental conditions.In this approach, the presented specimens are tested under quasistatic and cyclic tension load using in situ passive thermography and digital image correlation. In this way, damage progression like delamination growth can be monitored.Besides characterising hybrid samples during mechanical load, the samples are also tested before and after mechanical testing. Active thermography characterises defects in the CFRP component as well as defects at the interface of CFRP and thermoplastic whereas EMAT (electromagnetic acoustic transducers) characterise the interface between metal and thermoplastic.By combining EMAT and active thermography before and after mechanical testing the whole hybrid structure with its multiple interfaces can be examined for defects. The results are validated with computer tomography (CT).

Hendrik Jost, Michael Schwarz, Felix Grossmann, Jonas Sauer, Alexander Hell, Hans-Georg Herrmann

Resistance Welding of FRP to Steel Components in High-Volume-Production

Parts or Components made of fibre-reinforced plastics (FRP) are often connected to metallic components. However, joining FRP to metals is currently a particular challenge. As a rule, such connections are currently glued and/or mechanically joined. Recent research has focused on innovative hybrid connections, which are reinforced by small-scale 3D structures in the z-direction of the component axis. Although different approaches are being followed for the production of FRP/metal hybrids, there is still a great need for a joining process that meets the technical and economic challenges in this context.A new innovative joining concept, which is being worked on at the Institute of Welding and Joining Technology at RWTH Aachen University, is based on weldable inserts that are integrated into the manufacturing process of the FRP semi-finished product. As a result, these FRP structures can be joined locally with metallic connecting components using conventional resistance welding processes. The integration of the inserts is reproducible in the RTM process, which is suitable for large-scale production, and requires no post-processing. With the new joining process, high static composite strengths and a quasi-ductile post-processing behaviour can be achieved. Furthermore, the inserts can be freely varied in terms of the number of pins used and thus their arrangement can be adapted to the respective application.In addition to investigations of the static bond strength in different load directions, this paper also examines the failure behaviour of top-hat profiles and the combinability of the new joining technology with bonding processes.

Jens Lotte, Uwe Reisgen, Alexander Schiebahn

Novel Ultrasonic-Based Joining Methods for Metal-Plastic Composites (MPC)

The use of metal-plastic composites (MPCs) plays an important role for lightweight products. MPCs provide an innovative substitute for solid metal sheets due to their low weight, excellent stiffness, and due to their thermal and acoustic insulation. A challenge that links all the different applications is the need to efficiently process the MPCs at high quality and join them with other materials, using suitable joining techniques. Due to their special features (layer structure, material mix, etc.), conventional manufacturing processes are therefore only of limited or of no use at all. In particular, the polymer core layer is a barrier for the application of conventional joining methods. This contribution presents a novel joining approach for MPCs. The basic approach is the local melting of the polymer layer by energy of ultrasonic waves, and displacement of the molten plastic material by pressure on the cover sheets. Two different strategies are investigated for this purpose. In the first approach, the joining tool is directly superimposed by ultrasonic waves and the polymer is displaced before and during joining. In the second approach, the polymer layer is displaced in the joining area during a prior sheet forming process step. This paper describes the simulation of the ultrasonic-assisted displacement of the polymeric layer. These simulations are validated using experimental results. An exact analysis of the process parameters and infrared images are used for the validation of the simulation results. The results lead to an optimal design of special ultrasonic tools, which enable clinching and resistance spot welding in one step or allow pressing in a forming tool.

Matthias Riemer, Christian Kraus, Mathias Kott, Koen Faes, Marcin Korzeniowski, Marc Götz

Experimental Parameter Identification for the Bending Based Preforming of Thermoplastic UD-Tape

The combination of different types of plastics can be advantageous to obtain a good component performance at a reasonable price. For this, a compromise between mechanical properties and cheap manufacturing has to be found. In the research project GRK2078, the manufacturing of hybrid components consisting of long fiber reinforced thermoplastics (LFT) and unidirectional endless fiber reinforced material (UD-tapes) is researched. The LFT is the main constituent of the components. Local UD-tape reinforcements are added in areas with high load for a large effect or low geometric complexity to minimize preforming effort. To keep the cost low, a novel preforming process for the UD-tapes is in development at wbk Institute of Production Science. The aim is to enable the shape flexible, tool less forming of UD-tapes. To obtain this, the process is based on sequential bending of the UD-tape on several positions along its longitudinal axis during handling operations. To conduct the process, a supply unit and an industrial robot with a gripper with integrated heating devices are used. In this paper, the experimental examination of the process and the identification of suitable parameters on the shape of the preform are presented. The main influencing factors are the type of UD-tape, the heating of the tape and the movement of the robot. The processes are conducted with PA and PP carbon fiber tapes. The process quality with contact and radiation heating are compared and the respective heating duration is identified. For the robot movement, a kinematic description of the process is derived and compared to a circular bending movement. With the identified parameters, the process can be conducted reliably. The resulting accuracy limit and the process time with these parameters are described in this paper.

Daniel Kupzik, Alexej Bachtin, Sven Coutandin, Jürgen Fleischer

Design and Simulation

Frontmatter

Development of a Hybrid Crash-Relevant Car Body Component with Load-Adapted Thickness Properties: Design, Manufacturing and Testing

Semi-finished sheet products with load- or forming-adapted properties are classified as tailored blanks. By locally adjusting sheet thickness or material properties, the overall performance of the component can be improved while reducing the weight of the part. State-of-the-art tailored blanks are realized by rolling, welding or tailored heat treatment of monolithic materials and consider a change in properties with respect to the sheet plane. A further weight reduction could be achieved by combining the idea of tailored blanks with a multi-material design approach along the sheet thickness. For this purpose, a top-down material design is proposed to allow a demand-oriented hybrid tailored stacked blank design. Within this contribution an optimization-based top-down design methodology is applied on a crash relevant car body part. Based on benchmark crash simulations of a reference BIW structure, a critical body component is determined. The identified demonstrator component is later subdivided into multiple layers and submitted to an optimization loop in which the developed methodology varies the material parameters for each single layer. The result is a tailored stacked hybrid blank consisting of steel and FRP layers. In order to meet formability restrictions of the novel semi-finished product, the part under investigation is redesigned and compared with the reference BIW structure. Finally, the hybrid component is manufactured and tested on a dynamic crash device. Compared to a monolithic DP800 component, a mass reduction of 22% was achieved.

Alan A. Camberg, Thomas Tröster, Clemens Latuske

Operationalization of Manufacturing Restrictions for Hybrid Tailored Forming Components

In the Collaborative Research Centre (CRC) 1153, the process chain for the manufacture of hybrid high-performance components by Tailored Forming is being investigated. This involves the production of hybrid solid components. These have properties that are locally adapted to the respective load case, by combining different materials. The application potential of these multi-material components arises mainly where conventional mono-material components reach their technological development limits.However, the Tailored Forming process chain is more complex than conventional forming processes, as the combination of materials results in a larger solution space when designing components, because the distribution of materials must also be taken into account. Tailored Forming is also a new manufacturing technology whose fundamentals are currently being researched. So, there is only a small number of manufactured samples whose properties have not yet been adequately analyzed. As a result, few design guidelines are known to date according to which Tailored Forming components can be designed.In order to make statements about an optimized shape, the topology optimization method Interfacial Zone Evolutionary Optimization (IZEO) has been developed, which can be used to determine the material distribution for Tailored Forming components. Therefore, the manufacturing restrictions of Tailored Forming are numerically translated into geometric constraints that restrain the evolution throughout the optimization process. The solution achieved delivers a gross distribution of materials in the specified domain, while obeying the manufacturing constraints imposed. Further design development includes a fine construction of the model, where specific analysis can be executed about the joining zone of the different materials. With this process, the solution space can be efficiently explored and manufacturable designs can be produced, from which first guidelines for the construction of Tailored Forming components are derived.

Tim Brockmöller, Renan Siqueira, Iryna Mozgova, Roland Lachmayer

A New Numerical Method for Potential Analysis and Design of Hybrid Components from Full Vehicle Simulations: Implementation and Component Design

To exploit the lightweight potential of common materials like steel, aluminum or especially fiber-reinforcement plastics (FRP), a load-compliant material concept is mandatory. In keeping with the motto “the best material for the best application”, a new approach for a tailored material distribution between FRP and metals is proposed. By defining a scalar value referred as “uniaxiality” and a uniaxiality weighted sensitivity, a numerical method is implemented to identify body-in-white (BIW) components with a high amount of anisotropic loading. The uniaxiality value is gathered from full vehicle crash simulations and is superpositioned over all load cases to access a generalized information which component’s area is suitable for isotropic materials like metals and which one for anisotropic materials like FRP. In the next step, a functional component group consisting of an A-pillar and a roof frame section is exemplary engineered by using the findings of the numerical potential analysis. The developed extreme lightweight concept made of aluminum extrusion, unidirectional carbon fiber-reinforcement plastics (CFRP) tapes, warm stamped aluminum and press-hardened steel demonstrates outstanding performance that has been proven in full vehicle crash simulations and experimental tests. Furthermore, the concept is evaluated in terms of the components CO2 footprint and costs. Based on these data a scalable component concept is possible to meet customer specific requirements between the design objectives: lightweight, costs and environmental impact.

Thomas Tröster, Alan A. Camberg, Nils Wingenbach, Christian Hielscher, Julian Grenz

Graph Based Algorithms to Enhance Mid-Surface Design Fidelity of Finite Element Models of Extrusion Profiles

Extruded profile structures are widely used as efficient and lightweight crash energy absorbers in vehicle structures throughout the automotive industry. For the development and evaluation of new concepts and designs, finite element simulations are used to decrease costs and shorten development periods. In order to get good accordance between physical responses of extrusion profiles and their finite element representations under crash loads, a certain degree of modeling detail is needed. These details can be radii and material accumulations which are usually provided in volumetric CAD (Computer Aided Design) models. Leaving out these details in the profile cross section geometry can lead to differences in the buckling wavelength of walls and therefore in the deformation behavior.However, CAD designers are usually not incorporated into every design iteration of the CAE (computer aided engineering) departments and therefore these details might be missed out when design changes are rapidly imposed on a finite element shell mesh level. Furthermore, structural optimization methods applied to improve the profile’s mechanical behavior might not even allow for CAD designers to be involved. In this work two efficient yet simple to configure graph based algorithms to automatically apply rounded corners and to consider material accumulations at intersection points of walls of the profile are provided. These algorithms work with a graph based representation of the profile’s cross section geometry in order to perform geometric calculations. To describe the profile’s geometry the graph syntax of the optimization method “Graph and Heuristic based Topology Optimization” is used. Based on the graph a three-dimensional finite element representation of the profile is generated by an extrusion along a defined spline. This finite element model is the basis for further mesh modifications and conclusively for the simulation itself. The algorithms have proven their ability to increase the quality of the finite element representation of extrusion profiles and therefore increase the accordance between physical tests and simulation results in terms of geometry and result accuracy.

Johannes Sperber, Enrique Benavides Banda, Christopher Ortmann, Axel Schumacher

Backmatter

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